Three pipes A,B and C can fill a tank from empty to full in 30 minutes, 20 minutes
and 10 minutes respectively. When the tank is empty, all the three pipes are opened.
A, B and C discharge chemical solutions P, Q and R respectively.
What is the proportion of solution R in the liquid in the tank after 3 minutes?
(A) 5/11
(B) 6/11
(C) 7/11
(D) 8/11